I loved the Sweet Valley books.
I went to public school in the suburbs of Chicago and my high school banned sororities, fraternities and other secret societies. If there were any underground sororities or fraternities I didn't know about them.
More mentions of high school sororities and fraternities: there was a series of books I used to read called Sorority Girls, about a high school sorority called Pearl at a school in Michigan.
Here's a link to the description of the first book. (I think they are out of print now) Marjorie Sharmat also wrote a series of books called Sorority Sisters about two high school sororities. In non-fiction, Bob Greene mentions his high school fraternity, Epsilon (I think) in his book, Be True To Your School.